The title says it. What exactly is going on in your head? And more to the point does it do any short- or long-term physical damage (other than resulting from accidents that might occur)?
Your brain gets attitude and motion information from the three semi-circular canals in the inner ear. They are lined with hairs and filled with fluid. Motion in the fluid translates to pressure on the hairs, which then sends that information to the brain. When you spin around, the fluid motion overwhelms the brain’s ability to correctly sense your position.
How does that relate to motion sickness?
often motion sickness is worsened when your ear motion sensations doesn’t agree with your visual sensations.
seasickness is often worse when you have no view of the sea, if you watch the sea it can be less of a problem. reading or looking rearward or to the side in a car can make you car sick, looking out the window in the direction of travel can help.
When your brain gets conflicting information from your inner ear and your eyes, it gets confused. Motion sickness is the result.
You brain gets rotation information from the semicircular canals, which are indeed lined with hairs and filled with fluid. When the head rotates, the fluid tends to remain stationnary in space. This creates a ‘friction’ (here I approximate a bit) between the fluid and the canal itself, which is sensed by hair cells and generates a rotation signal. As an analogy, think that you are rotating a cup full of tea.
However, this fluid in quite viscous and pretty soon begins to rotate together with the canal (think about the tea cup again). After 5-10 seconds, the brain is receiving no more rotation information. At this point, if you are still rotating, you may feel a slightly unreal sensation since you see that you rotate but you inner ear doesn’t tell it to your brain. If you were rotated on a motorized chair in complete darkness, you would get absolutely unaware that you are rotating in about 30 s.
The dizziness comes when you stop. Indeed, as you stop, the fluid continues to rotate because of its inertia. Think about the teacup again: after a long period of rotation, the tea was rotating. Now that you stop the cup, the tea goes on rotating. This means that you get a signal which is the perfect mirror of the initial rotation signal. At this point you are not rotating but your brain thinks that you are. This so called post-rotatory effect creates the dizziness feeling.
Whenever the canals indicate a rotation, the brain will attempt to stabilize gaze by counterrotating the eyes. This is called the vestibulo-ocular reflex. In everyday’s life, this allows you to see sharp. After a prolonged rotation, the brain will constatly rotate the eyes although your head does not move. This results in a feeling that the world is spinning. In fact, the brain very quickly ‘sees’ the mismatch and the vestibulo-ocular reflex is supressed by about 90%, but the remaining 10% will still persist for about 20-30s.
About motion sickness:
- simple rotations in the dark on a motorized chair will not make you sick. You’ll just experience a feeling of motion which fades away. When you are stopped, you will experience a feeling of motion in the other direction.
- the same rotations in light may make you feel a little bad if you are sensitive, but this effect is rather limited.
However, trouble begin if you move your head after having rotated. Indeed, the post-rotatory sensation of motion is pretty harmless as long as you are feeling rotated around a vertical axis. But if you tilt your head a little, the motion signal created by the canals will remain ‘fixed’ relative to your head. The problem is that a rotation around a non-vertical axis is supposed to correspond to a rotation relative to gravity. For instance, if tilt your body forward and rotate leftward, you are supposed to be positionned nose-down relative to gravity after 90° of rotation. Your brain will anticipate this but it will not happen since you are in fact experiencing an illusory rotation. And your brain is going to be very unhappy about this. Indeed, while rotations around a vertical axis matter little for you postural system, correctly perceiving rotations relative to gravity is critical for maintaining balance.
As a result, when you just stand and spin and then stop, it is very likely that you will tilt your head a little without thinking about it, and you will experience balance difficulties. Furthermore the mismatch with your gravity perception (you also have gravity sensors in the inner ear) will cause motion sickness. In the lab, it is very easy to make someone sick this way.
Some similar but more complex effects happen if you tilt your head while rotating, this is why you can easily loose balance when you stand and you spin. In addition to the fact that your brain doesn’t receive motion information about the actual spin, the canals will also send some abberant rotation information whenever you tilt your head while spinning.
The vertigo associated with spinning makes sense. As people have explained, spinning messes up the fluid in your inner ear, screwing up your sense of balance.
However, scientists haven’t figured out yet why spinning can also cause nausea. I think the leading theory is that ingesting certain toxins can also trigger vertigo. So when you experience vertigo your brain says “Uh-oh! This may be a sign that we’ve been poisoned! Let’s empty the stomach to be safe!”
Or maybe it’s just a case of crossed wires, like the way that bright light can trigger a sneeze.
The cilia inside your labyrinthe canals detect that the fluid is moving, and part of the process that dampens the fluid motion is provided by small valves in the canals. If a cilia (cilium?) breaks loose and gets wedged in one of these valves, you have much less damping in that particular rotational axis. Net result: you’re constantly dizzy, with the fluid moving relatively unimpeded, and go stumbling along as if you’re drunk all the time. I had it; it was miserable. The doctors said that the cilia would eventually work itself free, and that one day I’d just notice that it was completely gone, which is what happened.
The spinning/dizziness effect can be reproduced by introducing cold or hot water into the external ear canal while you are lying on one side. The temperature difference deep in the ear (it has to get to the level of the eardrum to be really effective) causes a slight density difference in the fluid between the two sides of a semicircular canal: warmed fluid rises and cooled fluid sinks. This leads to the same effect as spinning your head in the horizontal plane, complete with involuntary jerking of the eyes and nausea. If cold water is used, the eyes repeatedly slide slowly toward the treated ear and then jerk quickly toward the untreated ear. If hot water is used, they turn slowly to the opposite ear and jerk quickly to the treated ear. If you have an intact brainstem and cranial nerves, the effect is quite strong and disorienting.
Medical students have been known to play this trick on their fellows who are caught sleeping.
I read a while back that the same inner ear balance mechanism that is responsible for seasickness also handles the body’s ability to detect ingested poison; the signals sent to the brain when a person is seasick are the same as those sent when a person has eaten something dangerous, and the body’s protective response to poison is vomiting. Therefore, when you’re seasick, you vomit. Does anyone know if there’s truth to this?
Okay, The Hamster King said something along similar lines, which I missed, but can anyone shed any more light on this?
Signals to the brain regarding our orientation come not only from the eyes. The body senses position by a variety of means, including the pressure on the bottoms of our feet. Seeing the horizon at an angle while standing straight up can be disorienting and is part of the explanation for seasickness. There, the conflict arises from visual, kinesthetic and vestibuar discrepancies.
Okay, so how do skaters manage to remain standing after one of those tornado-like spin maneuvers?
What makes you dizzy is not the velocity of the rotation istself, but its duration. Very fast but short (i.e. 2-3 s) rotations are not a problem.
Skaters also do longer duration figures, but they adapt to the disorienting nature of these motion by extensive training. Specifically, they learn to perform these highly stereotyped figures without really using their vestibular input. It has been shown that the VOR response (see my previous post) to vestibular stimulations is lower in figure skaters, indicating that the brain learns to ignore vestibular information. Here is one article on this topic; I didn’t find more on pubmed but I remember seing similar results at conferences.
Is it possible to train yourself to be less susceptible to motion sickness? Do astronauts acclimitize to free fall? (Are those two even the same?)
What if you fill that canal with a jello-like substance, thus making it unable to swirl? Will you have anti-dizziness protection? Or if instead you drained all of the liquid?
It would probably be a disaster.
The information from the inner ear makes it possible for you to move your head and have your eyes stay locked on target. Without that input, you would probably not be able to do something as simple as walking (or at least you would need extensive retraining) - your vision would be bouncing around.
There is one milder version of this operation, which consists in obstructing one part of the canal. The canal still retain some function, but the duration of the rotation signal during constant-velocity rotation is greatly reduced. This operation is used in some extreme cases of canal dysfuction, e.g. the vertigo reported by groo But let’s be clear, I’m speaking of rare cases where the symptoms don’t stop and the quality of life is severly reduced. Surgeons won’t cut around in your inner ear just for reducing motion sickness problems.
Completely losing the canals is not so terrible as losing the entire inner ear, which also contains gravity-sensitive organs (the otoliths). Those are critical for balance and you would really have problem unless you stick on firm, flat, clear and nicely adhesive ground. Forget about swimming too: it is utterly dangerous when you can not reliably tell where is ‘up’.
Losing the vestibular organs has sometimes another adverse effect, which is visual vertigo. The brain compensates the loss by becoming increasingly dependant on visual input for orientation. A consequence is that unnatural inputs, such as sitting in a train an looking through a window, or watching a waterfall, can create strong vertigo attacks.
You train yourself by learning what actions make it worse and advoid them. When at sea I do not drink coffee. When I fly when they are bring around drinks I always get ginger ale. When the pilot turns the plane down to land I quit reading and sit up straight. I keep the AC blowing in my face on high and I never wear a hat on the plane or my jacket. And a big one no matter if I have a cold, or allergies I never take antehistimans.
The poison thing I felt was interesting because when I get motion sickness I fill like I have been poisoned. I can fill it in my whole body.;
My wife has severe motion sickness, which I think is mostly psychological, maybe connected to an overall fear of flying.
Just before a flight, she will get nauseous in any sort of travel, such as riding the car on the way to the airport.
However, after taking Dramamine, she has trained herself to ignore motion sickness, and this has also affected her psychologically.
Therefore, in my experience, if your motion sickness is mostly psychological, then yes, you can train yourself to be less susceptible to it.
Will champaign make you dizzy?
Yes, but the name’s Daisy!